HAWC observations of the acceleration of very-high-energy cosmic rays in the Cygnus Cocoon

TL;DR

This paper reports HAWC observations of gamma rays from the Cygnus Cocoon, indicating it as a source of very-high-energy cosmic rays up to 1 TeV, suggesting star-forming regions can accelerate particles to these energies.

Contribution

It provides the first evidence that star-forming superbubbles like the Cygnus Cocoon can accelerate cosmic rays to TeV energies, challenging previous assumptions about cosmic ray sources.

Findings

Detection of 1-100 TeV gamma rays from the Cygnus Cocoon.

Evidence of hadronic interactions producing gamma rays.

Spectral and emission profile changes indicating cosmic ray transport.

Abstract

Cosmic rays with energies up to a few PeV are known to be accelerated within the Milky Way. Traditionally, it has been presumed that supernova remnants were the main source of very-high-energy cosmic rays but theoretically it is difficult to get protons to PeV energies and observationally there simply is no evidence to support the remnants as sources of hadrons with energies above a few tens of TeV. One possible source of protons with those energies is the Galactic Center region. Here we report observations of 1-100 TeV gamma rays coming from the 'Cygnus Cocoon', which is a superbubble surrounding a region of OB2 massive star formation. These gamma rays are likely produced by 10-1000 TeV freshly accelerated CRs originating from the enclosed star forming region Cygnus OB2. Hitherto it was not known that such regions could accelerate particles to these energies. The measured flux is likely originated by hadronic interactions. The spectral shape and the emission profile of the Cocoon changes from GeV to TeV energies, which reveals the transport of cosmic particles and historical activity in the superbubble.